1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a device and method for transporting printed products.
2. Background Information
U.S. Pat. No. 5,447,302 purports to disclose an apparatus for removing paper products from a stack on a hopper. The apparatus has a rotatably mounted gripper drum which rotates about a central axis at a constant angular velocity. A stationary cam is rigidly mounted adjacent the gripper drum. A cam follower follows the outer side of the cam, and is attached at one end to a link, which also rotates with the gripper drum. The rotating link is pivotable about a pin, so that a variation in the cam radius can cause the link to pivot, so that an other end of the link compresses or stretches a spring. This other end of the link connects to a further link which can retract a toggle arm on which a gripper and a gripper seat are supported. If the toggle arm is pulled so that the gripper and the gripper seat accelerate in the same direction as the movement of the gripper drum, the gripper is opened. If the gripper and the gripper seat are slowed down relative to the gripper drum, the gripper is closed.
The device of the ""302 patent has the disadvantage that the link structure is complicated, especially in that a spring is required to force the cam to follow the cam follower. The repeated compression and expansion of the spring can lead to a weakening of the spring over many rotations and can cause the entire apparatus to malfunction. At high speeds, high spring forces must be maintained to keep the cam follower on the cam and the gripper from engaging properly. Departure of the follower from the cam can cause gripper malfunction or damage.
Moreover, the gripper force remains relatively constant regardless of toggle arm displacement. A large gripping force thus is necessary for thick products, which can then damage thin products if they are used on the same machine.
An object of the present invention is to provide a rotating gripper drum which is durable and which has improved high speed operating characteristics. An additional or alternate objective is to provide a reliable rotating gripper gripper drum. Another additional or alternate objective is to provide a method and device for gripping with increased gripping force as product thickness increases.
The present invention provides a gripper drum device comprising a drum body rotatable about a central axis, an actuating shaft rotatable within the drum body, a box cam follower connected to the actuating shaft for moving the actuating shaft, a gripper seat connected to the actuating shaft, a gripper connected to the actuating shaft, and a box cam, the box cam follower being located within the box cam for following the box cam.
The box cam of the present invention controls and limits the movement of the cam follower, and eliminates the need for a spring to force the cam follower.
Advantageously, a gripper seat may be moved about a first axis by a first link to the cam follower, and the first axis being different from an axis of the actuating shaft. The actuating shaft preferably is connected to the gripper by a second link.
By separating the link between the actuating shaft and the gripper seat from that between the cam follower and the gripper, gripping movement can be better controlled, so that, for example, a smoother pick-up of printed products can be obtained.
Advantageously, the second link connects directly to the cam follower and drives a rack of a rack-and-pinion mechanism, the pinion being connected to the gripper. The gripper seat preferably is connected directly on the first link, which is driven by a support link connected directly between the first link and the cam follower.
The gripper preferably is spring-loaded, in that a spring is located directly between the spring and a spring support attached to the rotating drum. Because the spring in the present embodiment acts only against the gripper, it may be compact and not suffer acceleration distortions which had been present in the prior art. Moreover, because the spring acts solely on the gripper, the gripping force advantageously may be increased as the gripped product becomes thicker. This permits a small initial load to be applied for thin products, and results in less damage to these products. Less wear of components and less required torque for the entire system thus is also results.
The present invention also provides a gripper drum comprising a drum body rotatable about a central axis, a gripper movable at an outer circumference of the drum body, a gripper seat for interacting with the gripper, and a cam follower connected to the gripper seat by a first link and connected to the gripper by a second link different from the first link.
The present invention also provides a method for gripping printed products including the steps of rotating a drum about a central axis, moving a cam follower within a box cam, and gripping a printed product with a gripper attached to the cam follower.
The term xe2x80x9cbox camxe2x80x9d as used herein is defined as a cam having a groove or slot in which a cam follower rides and which constrains the cam in both a radially outward and radially inward direction.